The present invention relates generally to envelopes and more particularly to a tamper detection envelope which cannot be opened once it is closed without leaving visible evidence that the envelope was tampered with. Such envelopes are known in the prior art but many are unreliable in use. For instance, some of the known tamperproof envelopes can be steamed open and then resealed without leaving behind visible evidence of the tampering. These envelopes do not rely on the actual severing of portions of the closure flap as disclosed herein, but rely instead on the critical location of certain cut segments which in most cases can be relocated in their proper place after opening by a careful thief.
Examples of prior art tamper detection envelope structures are shown in U.S. Pats. Nos. 190,630; 544,277; 712,465; and 2,128,196. In each of these prior patents, incisions are cut in the envelope closure flaps to produce flaps or designs for showing evidence of tampering. In contrast to these teachings, the present invention employs a different means for tamper detection by using a method that induces the actual tearing of portions of the flap structure when the envelope is tampered with.